GEA - a sprawling group of more than 100 companies where many own significant stakes in one another - is so far facing two public acquisition offers led by Grupo Gilinski.

The contretemps with banker Jaime Gilinski - one of Colombia's richest men and the owner of GNB Sudameris, among many other businesses - is shaking up GEA's previously quiet conglomerate of tightly interwoven holdings, an arrangement that had until recently protected it from takeover attempts.

GEA groups many of Colombia's most important companies, including food producer Nutresa, industrial conglomerate Grupo Argos, bank Bancolombia, cement-maker Cementos Argos, energy generator Celsia and pension fund Proteccion.

Investment holding company Grupo SURA, which owns 20% to 50% stakes in many of the other GEA companies, is the jewel in its crown.

Gilinski launched a public acquisition offer for up to 62.625% of shares in Nutresa, a purchase worth some $2.2 billion, in November with the backing of Abu Dhabi's Royal Group.

Gilinski who has given few interviews, has told local media he thinks the company is simply a good investment.

Royal Group, an investment company chaired by Tahnoon Bin Zayed Al Nahyan, the United Arab Emirates' national security advisor, will hold 49.9% of the shares bought through the offer, while Gilinski will control the rest.

The offer for Nutresa was unprecedented on the Colombian market, both for its size and for attempting to move on the behemoth GEA. It has been extended until Jan. 12.

The market was further shocked three weeks later when Gilinski made another offer for up to 31.68% of Grupo SURA, at a cost of up to $1.19 billion, according to Reuters calculations of stock market data.

Both Argos and SURA have ruled out selling any of their stakes in Nutresa to Gilinski.

They said after the offer announcements they would seek international minority partners and they consider Gilinski's offers - especially for Nutresa - to be below market value.

"It's a very hostile scenario for the (GEA) group," said Laura Triana, analyst at Acciones y Valores brokerage. "This way, Gilinski really limits the possibilities for Grupo SURA and Grupo Argos to cover themselves because he's coming in from two fronts."

Gilinski will hold all shares bought through the Grupo SURA offer, which is aided by financing from the First Bank of Abu Dhabi, according to the formal offer announcement published on Thursday.

IHC Capital Holding LLC, also controlled by Al Nahyan, has signed a letter of intent with Gilinski to potentially act in future as a capital partner in his Grupo SURA participation, pending regulatory approval, the document showed.

The SURA offer will take place between Dec. 24 and Jan. 11.

Though major shareholders like other GEA members could make counteroffers - especially if they managed to raise funds from international partners - the clock is ticking and Gilinski's financial muscle is stronger thanks to his Royal Group backing, analysts told Reuters.

"The authorization by the financial regulator for the initial public offering for Nutresa came so fast that I'm not sure how quickly a counteroffer strategy can be pulled together," said independent analyst Daniel Escobar.

Nutresa's share price has risen nearly 30% since Gilinski announced the acquisition offer, but it is still below the $7.71 per share he is offering.

Many in the market say Gilinski is undervaluing Nutresa and SURA, criticisms also leveled by SURA and Argos, which cited independent valuations by major banks.

"Gilinski isn't paying a control premium, it's almost a fair share price, and in these hostile buying operations normally the prices are higher," said Escobar.

Trading of Grupo SURA shares haa been suspended pending the formal announcement of the offer, but will resume on Friday.

Gilinski's son Gabriel told Reuters he could not comment until after the public offers have finished. Spokespeople for Grupo SURA, Grupo Argos and Nutresa declined to comment.

Argos has also said it will speed efforts to consolidate several investments in road and airport concessions, energy and real estate into one vehicle that it hopes to list on the New York Stock Exchange.

Analysts said an offer for Argos itself could also be in Gilinski's plans and that the public offers may also be the first step for him to regain a lost asset - Bancolombia bank.

Grupo Gilinski sold the bank, then called Banco de Colombia, to GEA in 1997. A dispute about how the payment was made led to more than a decade of civil lawsuits, which finally ended in 2010 with an agreement between the two companies.

Two brokers who have spoken to Grupo Gilinski staff handling the public offers told Reuters on condition of anonymity that though Gilinski's principal focus is accumulating stakes in GEA companies, his desire to reach Bancolombia through the Grupo SURA offer is evident.

"When you listen to them the hostile tone is notable... they are going after it all," said a broker involved in the Nutresa offer. "If Gilinski manages to buy, he'll be in the group and in the future he can go for Bancolombia."

Grupo SURA owns about 46% of Bancolombia shares.

Bancolombia had no comment.

(Reporting by Nelson Bocanegra; Writing by Julia Symmes Cobb; Editing by Nick Zieminski)

By Nelson Bocanegra